The present invention relates generally to explosive shaped charges and, in an embodiment described herein, more particularly provides an oilwell perforator having a metal coated high density metal powder liner.
Oilwell perforators are used to perforate casing or liner lining a wellbore, to thereby provide a path for production, or injection, of fluids therethrough. In order to achieve an acceptably deep perforation tunnel in hard rock having high density and high compressive strength, it is generally recognized that it is desirable to form a liner of an oilwell perforator from a relatively dense material.
In general, deep penetrating oilwell perforators have liners made of partially sintered metal powder, or blends of various metal powders. If different metal powders are used, extreme care must be taken to prevent segregation of the different powders. This segregation may be due to different particle shapes, densities and sizes in the different powders. A liner made of segregated metal powders is undesirable because it will not form an appropriately shaped metal jet when the perforator is detonated.
A metal powder having a suitably high density for use in a deep penetrating perforator is made up of tungsten metal particles. Unfortunately, the tungsten particles in the powder are relatively hard, and so the particles do not readily adhere together when the powder is pressed into a liner shape. The ability of a pressed metal powder to resist deformation prior to being partially or fully sintered is known as the xe2x80x9cgreenxe2x80x9d strength of the pressed powder.
A sufficiently high green strength is required for handling and other manufacturing processes. A present solution to the problem of low green strength in liners made from tungsten powder is to blend the tungsten powder with other metal powders which, although they may be less desirable in some respects than tungsten for use in deep penetrating perforators, enhance the green strength of the pressed metal powder. Due to the presence of the other metal powders in the liner, segregation problems occur and the tungsten content of the liner is reduced to less than about 95% of the liner by weight.
Therefore, it may be seen from the foregoing that it would be desirable to provide a perforator with a liner that has an increased proportion of tungsten or other high density metal therein and which has a reduced tendency for segregation of metal. powders therein, but which has sufficient green strength.
In carrying out the principles of the present invention, in accordance with an embodiment thereof, a shaped charge is provided which includes a liner formed from metal coated high density metal powder. A method of using the shaped charge as a perforator in a well is also provided.
In one aspect of the present invention, a perforator is provided which has a liner formed of a metal powder wherein particles thereof are coated with another metal. The metal powder may be tungsten and the metal coating may be, for example, copper, lead, molybdenum, tin, nickel or silver. The metal coating enhances the green strength of the liner and significantly reduces the possibility of segregation of the metals as opposed to a mere blending of metal powders.
In another aspect of the present invention, a perforator is provided which has a liner formed of a tungsten powder wherein particles thereof are coated with a less dense metal. Nevertheless, the liner has an increased proportion of tungsten therein, and therefore has an increased density as compared to conventional liners with tungsten powder therein, and the metal coating permits the tungsten powder particles to be pressed into a liner shape with sufficient green strength.
These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of a representative embodiment of the invention hereinbelow and the accompanying drawings.